Date of Award

Fall 2013

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering - (M.S.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

N. M. Ravindra

Second Advisor

Halina Opyrchal

Third Advisor

Tao Zhou

Fourth Advisor

Ken Keunhyuk Ahn

Abstract

Utilizing the two-band approximation and Wentzel-Kramers-B ri l l oui n (WKB) approximation, by including the temperature-dependent effective masses and nonparabolicity effects, an investigation of the temperature dependent band-to-band tunneling process is discussed. In comparison with the parabolic approximation and non- parabolic approximation, the tunneling probability is strongly dependent on the non‑ parabolicity factor. The temperature dependence of the energy band gap, electron effective mass and light hole effective mass is investigated. The tunneling current density function is derived by a series representation of the incomplete gamma function with non-parabolic effect and its variation at low temperature is also investigated. When the Fermi level of holes is in excess of that of electrons, i.e., EFp>>EFn, the current density function can be successfully simplified as the Fowler-Nordheim formulation. The quantum efficiency model, for CIGS solar cells, is discussed. Device modeling and simulation studies of a Cu(In1−x,Gax)Se2 (CIGS) thin film solar cell are carried out. A variety of graded band-gap structures, including space charge region (SCR) grading, back surface region grading, and double grading of the CIGS absorber layer are considered. A position-dependent absorption coefficient α(x, hv) is obtained by a differential equation for the photon flux φ(x, hv). The quantum efficiency can be calculated by IQE=(φ1-φ2)/φ3. The temperature dependence of the quantum efficiency is also investigated in this thesis.

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